IMPORTANCEPosttraumatic stress disorder (PTSD) in elderly men may be associated with increased risk of Parkinson disease (PD); thus, this group of patients needs to be monitored closely for timely, customized treatment. OBJECTIVE To evaluate the risk of PD in patients with PTSD compared with patients without PTSD. DESIGN, SETTING, AND PARTICIPANTS This population-based, retrospective, cohort study used data from Maccabi Health Care Services (MHS), the second largest health plan in Israel, spanning from 2000 to 2019. Participants included MHS members born before 1970 who received a diagnosis of PTSD in 2000 to 2015. Patients with PTSD who had PD before their first diagnosis were excluded. Data analysis was performed from February to June 2022. EXPOSURES Incident PTSD was denoted by at least 1 diagnosis (1) given by psychiatrists, psychologists, or neurologists; (2) hospital discharge diagnosis; or (3) registered as a chronic diagnosis (defined as such by the primary care physician). The index date was defined as first diagnosis for the patients with PTSD and for the corresponding patients without PTSD. MAIN OUTCOMES AND MEASURES PD incident cases up to 2019 were ascertained by idiopathic PD diagnosis (1) given by a neurologist, (2) extracted from a hospital discharge report, or (3) registered as a chronic diagnosis. Patients with PD-like syndromes documentation after the last mention of PD were excluded. RESULTSOf 8342 eligible patients, 8336 (99.9%) were matched to nonexposed patients in a 1:1 ratio by birth year and sex; 4303 patients (51.6%) were male, and the mean (SD) age at index was 55.8 (13.2) years. Patients with PTSD had a 1.48-fold (95% CI, 1.10-1.99) excess risk for PD, compared with patients without PTSD. An elevated risk of PD (hazard ratio, 1.95; 95% CI, 1.16-3.28) was recorded among men receiving a diagnosis of PTSD at age 72 years or older. CONCLUSIONS AND RELEVANCEThese findings suggest that elderly men who receive a diagnosis of PTSD are at an increased risk of PD. Further studies are needed to corroborate these findings and to further assess the association of stress with PD risk.